Laterally double-diffused-metal-oxide semiconductor (LDMOS) transistors have the characteristics of high break-down voltage, and compatibility with the complimentary MOS process; and have been widely used in power integrated circuits (ICs). Conventional MOS devices include source and drain that are symmetrical with respect to a gate structure, while, in a LDMOS transistor, the distance between the drain and the gate structure is greater than the distance between the source and the gate structure. Specifically, there is a relatively long lightly-doped region between the drain and the gate structure of the LDMOS transistor. Such a path is referred to as a drift region. When a high voltage is applied to the drain of the LDMOS device, the drift region is used to sustain a relatively high potential to obtain a relatively high breakdown voltage (BV).
The drive current (Ion) and the breakdown voltage are the two important parameters to evaluate the electrical properties of the LDMOS devices. The drive current refers to the current flowing from the drain to the source of the LDMOS device when the LDMOS device is in operation. The breakdown voltage refers to the maximum transient threshold voltage of a targeted terminal of the LDMOS device before the LDMOS device is broken down. A relatively large drive current and a relatively large breakdown voltage enable the LDMOS device to have a desired switching characteristic and a relatively strong drive ability.
However, it is desirable to improve the electrical properties of conventional LDMOS devices. The disclosed methods and semiconductor structures are directed to solve one or more problems set forth above and other problems in the art.